Process for treating lead



I May 13, 1941'. H. M. BURKEY' PROCESS FOR TREATING, LEAD Filed Aug. 2, 1940 I EFF/501,875;

DROSJ MET/IL A/YD /l//? INVENTOR. ffiR E MEuR/rA-K BY km v /M ATTORNEY.

Patented May 13, 1941 PROCESS FOR TREATING LEAD Harvey M. Burkey, Plainfield, N. J., assignor to The American Metal Company, Limited York, N. Y., a corporation of New York New Application August 2, 1940, Serial No. 349,530

(Cl. 75-78) T 6 Claims.

This invention relates to separating tin from impure lead containing tin and perhaps other components, and particularly to such separation by oxidation through stirring.

Separation from lead of relatively small quantities of tin, arsenic, antimony, copper, etc. by the so-called softening method is known. Another method for separation of tin from lead and other components by air oxidation with stirring to produce a low tin content dross is also known. These processes start with ya bath of lead containing tin and other components, respectively, in a softening furnace or kettle and oxidation of the surface of the bath produces a dross containing lead oxide and some tin oxide. The maximum quantity of tin that could be recovered in the dross by these known processes, according to published statements, is about 12.5% of tin oxide, representing approximately 9.5% of metallic tin. More recently, a process has been described in the patent of Harper and Reinberg, No. 2,155,545, granted April 25, 1939, which removed tin oxide in a dross produced by stirring a clean bath of molten metallic lead containing tin and other components. It accomplished a faster removal of tin than the previous stirring process and instead of producing a dross containing a maximum content of approximately 12.5% tin oxide, it produced a dross which under preferred working conditions ran as high as about 45 of tin.

The principal object of the present invention is to provide a simple process for separation of tin from impure lead which shall possess advantages over the known processes. The invention accordingly comprises the novel processes and steps of processes, specific embodiments of which are described hereinafter by way of example and in accordance with which I now prefer to practice the invention.

It is important in eflicient commercial operations for recovering tin, for example, from lead, that the cost of the operation shall be kept as low as possible for the particular purpose in hand. Thus, if the rate of tin removal is the most important factor, the process for remov-- ing the tin should be capable of doing so at the highest possible speed. On the other hand, if the production of a high tin content in the resulting dross is the more important factor, then the process should be capable of producing such high tin content. In other words, a control of the tin removal process for eflicient operation should be readily availabe to the operator to vary the removal accordingly as a high speed removal with low tin content, or a low speed removal with'high tin content, is desired. My invention as herein set forth not only permits such control not heretofore known, but, so far as I am aware, is capable of producing from impure lead, a higher tin content in the dross than can be obtained by any of the known processes.

It is also possible in accordance with my process to control the amount of lead oxidized and removed from the bath during the process by the quantity of litharge employed. Thus, I may conduct the process so that large quantities of lead are removed or so that the quantity removed is reduced to approximately zero. In addition, I may even reduce lead from the dross sufliciently so that the total amount of lead in the bath is increased by the process, if desired.

Two types of oxidation occur when a bath of impure lead containing tin and other impurities, such as antimony, arsenic, etc., are stirred at high temperatures and high speeds, for example, at temperatures of above 950 F. and stirring speeds of at least 900 R. P. M. in an apparatus of similar proportions to that shown in the drawing accompanying this application, below referred to. One of these types is an oxidation by air to form litharge, which is lead oxide, antimony oxide, etc. The second type of oxidation occurs by what is called a "replacement reactio Each of these reactions occurs, as is known, during the stirring process mentioned above. I have found, however, in accordance with my invention, that the more important of these reactions is the latter-mentioned one, namely, the replacement reaction, and I have found that it is important to continue the pro'cess throughout so that substantially the maximum amount of replacement reaction for a given tin content of dross occurs.

Chemically, the air-oxidation and replacement reactions mentioned may be expressed as folows:

(metallic (oxygen) (lead oxide) lead) Sn 02 SnOz (metallic (oxygen) (tin oxide) Antimony, arsenic, etc. are similarly air-oxidized.

bath) J Other metals contained in the dross, such as antimony and arsenic, may react similarly and I to make a few simple litharge, a dross is taken remainder being substantially litharge,

j the content of. tin in the dross refer to such reactions as replacement reactions.

In the first two reactions air-oxidation is represented, and in the third reaction replacement reaction is occurring; that is, the litharge formed by reaction (1) is reacting with tin in the bath to form metallic lead and tin oxide. I have found that if I start my process by placing on top the impure lead, then or previously melted, a layer of finely divided litharge of about two inches in thickness, and stirring at the speeds and temperatures mentioned above, then both the replacement and air oxidation reactions occur from the start of the process. The replacement reactions occur because the litharge is stirred into the bath to form metallic lead, which then joins the metal below, and tin oxide, which joins the lead oxide on top. The air penetrates through the interstices in the litharge on top of the bath which is then stirred into the bath along with the litharge. While the litharge is forming tin oxide and being reduced to the air is in turn forming more litharge from the bath to replace that which has been used up to oxidize the tin.

-The amount and purity of litharge placed on top of the bath, other factors being the same, controls the rate at which tin is removed and the percentage of tin in the dross produced, as well as the amount of lead removed or added to the metal being treated. Additions of litharge at the start in amounts of about 1 to about 5% of metal treated increase the speed of tin removal and reduce the time required for the operation. If the factors other than the amount of litharge added are varied, there will be corresponding variation required in the amount of lithargeemployed for any given set of conditions. Thus, the size of the apparatus and operating conditions employed and the amount of tin content of the metal treated are factors which will influence the speed of the tin removal and the time required. I have described below the results of varying amounts of litharge added for a given set of conditions. It is a simple matter in case these other factors are changed somewhat tests on the amount 'of litharge to give the results desired employing the changed conditions of operation to determine what is the amount of litharge to be employed.

With a litharge which issubstantially pure and contains, therefore, substantially no tin, the rate of tin removal from the bath is relatively high, but the resulting dross after a period of three or four hours will have an intermediate tin content. That is, it may have 30% to.,40% tin as oxide. On the other hand if instead of using a pure which contains a high of tin as oxide, the then under the same conditions as those where the litharge alone was employed, the rate of removal of tin from the bath will 'be slowed down, but will be maintained at a high point, say, over 40% of tin as oxide. In between these figures of, say, litharge with zero per cent tin and litharge containing tin, for example, but without limitation, of 40% or more, it is possible to vary the rate of removal 'of tin quantity of tin, say 40% h from the bath and to maintain the tin content at substantially any desired level.

An apparatus in which the process may be carried out is shown in the accompanying drawing constituting a part of this specification, in which the figure is a vertical section. shown in metallic lead,

part diagrammaticallmof a kettle with a stirrer mounted thereon.

In the drawing, the numeral I indicates a hemispherical steel kettle of about 86 inches in diameter in which is contained a bath 2 of molten lead containing tin and which may also contain other components such as antimony, "arsenic, copper, silver, etc. Mounted above the bath on suitable supports 3 is a high-speed electric motor 4. This motor operates a vertical shaft 5 which, depends therefrom and at the end of which is mounted a disintegrating impeller 6. The impeller is placed preferably at about one half the depth of the bath 2. The motor 4 is capable of rotating the shaft and impeller at speeds of 900 R. P. M. or higher, giving a peripheral speed of the impeller of over about 2600 feet. per minute where the impeller has a diameter of about 9 inches as shown. The impeller 6 comprises a sleeve keyed to the shaft 5. From the sleeve and integral therewith may extend four disintegrating radial arms 'I of generally elongated pyramidal shape in plan view. Each outer end of each arm may terminate in two fiat disc-like faces 8 providing a leading flat'face is rotated. A burner 9 passes into the housing at the base of the kettle and is used for initially heating'the contents and maintaining the heat of the kettle when required. When the motor 4 is operating at 6 to form a vortex I0 in the molten metal of the bath 2.

In carrying out my process, I introduce into the kettle I a quantity of lead containing tin, and perhaps antimony, arsenic, etc. and heat it, if necessary, to render the mass molten. I then add a layer I I of previously prepared lead oxide to this bath to a depth of approximately 2 to 3 inches. This lead oxidemay be finely divided pure litharge if desired or it may be a similar quantity of very finely-powdered dross from 'a previous run; that is, a quantity of dross which may be left in the kettle with a small heel" of metal after pumping out the detinned molten lead. The motor 4 is then'started to give the stirrer 6 a speed of above about 900 R. P. M. and the temperature is maintained above about 950 F. but below the complete fusion temperature of the lead oxide or dross layer. Atthe speeds mentioned, a vortex is produced as shown in the drawing. The layer containing lead oxide descends to the impeller, is disintegrated-and scattered through the molten bath from the beginning of the operation. The 'lead oxide particles thus thrown into the bath react with metallic tin'to produce metallic lead and tin oxide. The latter. floats to the top of the bath and joins the layer II. In'this way the tin builds up as'tin-oxide in this circulating layer. The thickness and fineness of the layer is such that air is admitted through the spaces between .the particles of lead. and tin oxide and other oxides such as antimony, arsenic, etc. to react with the bath and produce an addi tional quantity of"lead oxide, which then joins the layer I I and' is circulated with it to produce further quantities of tin oxide and lead.- The reaction between tin and leadoxide aswell as that between lead and air produces heat and, accordingly, it is not necessary to continuously apply heat to the metal bath to keep it in molten condition. 'But ordinarily it has been found that some heating should be applied from time to time and this may be'done by the burner 9.

The following examples represent preferred embodiments of the invention. It is to be unwhen the impeller high speed, it causes the impeller about 9 inches.

ples, a previously prepared layer about 2 inches.

in thickness of litharge or dross or similar lead oxide containing layer, which is in finely powdered condition, is placed on the bath of molten lead to be detinned. The stirrer is then started and both the stirring speed and the temperature are maintained as indicated in the examples. It will be understood that kettles ofvarious shapes and sizes may be employed in carrying out the invention. I have found it preferable to employ one of the hemispherical shapes shown in the accompanying drawing. In tests which I have made in this apparatus as shown, I have found that the rate of removal will vary according to the ratio of the impeller to'the kettle size. For example, with a kettle having a diameter of about 41 inches and an impeller having a. diameter of about 6 inches, the removal is about twice as fast as with a kettle having a diameter of about 86 inches and an impeller with a diameter of The following examples have been conducted with kettles and impellers for both the ratios mentioned. In Examples 1 and 2 below, the kettle" has a diameter of about 41 inches and an impeller with a diameter of about 6 /2 inches. In Examples 3 and 4,'the kettle has adiameter of about. 86 inches and the impeller about 9 inches.

EXAMPLES Example 1 To a kettle containing 7360 lbs. of impure lead was added 190 lbs. of substantially pure litharge. The metal was stirred for one hour and two and one-half minutes (at which time all tin had been removed) at a speed of 1700 R. P. M. and a temperature of 1020 F. to 1160F. At the end of the run, 460 lbs. of dross was removed.

The assays ofthe metal at the start and end were as follows:

Weight Sn s'b As Ag Pb Ounces Per- Percent Percent Percent per ton cent Start 7,360 1.32 6. 79 0. 39 102.8 91.12 End 7,110 Trace 6. 65 .38 103.6 92. 59

The dross at the start was commercially pure litharge and at the end assayed as follows:

Weight Sn Sb As Ag Pb Ounces Percent Percent Percent per trm Percent 460 23.05 7. 27 0.18 56.3 58. 75

The details of tin removal on the basis of metal analysis were as follows:

Tin removal on'basis of dross assays were as follows:

Rate of tin removal Pep Pounds Pounds Time 31 3 cgnt Ja P 6 Pounds n oun s per tamed metal per hour 'hour per ton metal Start 190 0 0 0 Ewample 2 v To a kettle containing 7,245 lbs. of impure lead was added 420 lbs. of dross containing 28.57% tin. The metal was stirred 1 hours at a speed of 1700 R. P. M. and a temperature between 1020 and 1140 F. At the end of the run, 590 lbs. of dross was removed.

The assays of the metal at the start and end were as follows:

The dross at start and finish assayed as follows:

Weight Sn Sb As Ag Pb Ounces Per- Percent Percent Percent per ton cent Start 420 28. 57 6. 16 0. 18 48. 4 61. 5 End 590 37. 49 5. 36 26 43. 5 46. 70

The details of tin removal on the basis of metal analysis were as follows:

Rate of tin removal Pounds Pergg Pounds Time in cent com tin re- Pounds kettle Sn mined moved Pounds per per hour hour per ton metal 1. 34 97. 08 27 19. 28 77. 77. 80 21. 49 Trace 97. 08 64. 7 17. 87

Tin removal on the basis of dross assays was as follows:

Rate of tin removal Pounds Pounds P Per tin tin Pounds Time in cent com per kettle Sn tained moved ag hour hour gs;

metal Example 3 g A charge of 82,000 lbs. of impure lead was pumped to a'kettle, to which was added 965 lbs. of oxide dross from a previous kettle charge.

The analysis of metal and oxide dross at the start were as follows:

Weight Sn Sb As Ag Cu Pb Par Par Per Ounces For For Pounds cent cent cent per ton cent cent Metal 82, 000 l. 53 14. 73 1. 18 4 10 Bel. Dross 11. 84 25.13 1. 49. 70

After another A of an hour stirring, the tin was down to atrace in the metal and 3236 lbs. of

dross was skimmed and sampled.

.The temperature ranged between 1110 and 1170 F. and the stirring speed was about 1700 to 1800 R. P. M. using an 80 H. P. motor.

The analysis of the metal and final dross at end of run were as follows:

Weight Sn Sb As 1 Ag Cu Pb Per Per Per Ounces Per Per Pounds cent cam cent per ton cent cult Metal 80,000 Trace 14.41 1.12 4. .10 B Dress 3,236 39.25 9.00 .87 36.52

The-details of the tin removal on the basis of metal analysis were as follows: a

Tin removed Pounds Per a -E 'i g Pounds Time lead in cent com Pounds lper keme Sn tained moved per ton of metal Start 82,000 1. 53 1255 At 1 hr 81, 300 96 780 475 475 1l. 58 At 2 k 11!. 80, 400 53 426 829 332 8. At 3% h! 80, 200 26 209 1046 322 7. 85 At 4 hi 80, )0 Trace 1255 314 7. 65

As a check,.the tin removal on the basis of dross removed is shown below:

Tin removed 1 Pgunds Per Poiimds Pounds Pounds Time ross cont t n tin per 111 Sn conre- Pounds hour kettle tamed moved per pet rhour ton of metal Start 965 11. 84 114 At 1 hr 1795 29. 53 530 416 416 10. At 2' hr 2535 38. 38 973 859 343 8. 37 At 3 hr 2910 38. 00 1106 992 305 7. 43 At 4 3236 39. 25 1270 1156 289 7. 05

The variation in the comparison of rates of tin removal in these check tests in this example is due to differences in sampling, weights, dust losses, etc. The same remark applies to Examples 1 and 2. v

Example 4 To 'a kettle containing saooo lbs. of lead was added about 1500 lbs. of dross containing 47.12% tin. The metal assayed 1.3% As, 120 oz. per ton Ag, 25% Cu and the balance lead.

After stirring six hours at 1700 to 1800 R. P. M.

2535 lbs. of dross Sn, 5.02% Sb, 22%

50.34% Sn, 2% Sb, .1% As, 35 oz. per ton Ag, .1% Au and 33.4% Pb.

The rate of tin removal based on metal assays was 76.5 lbs. per hour or 1.84 lbs. per hour per ton of metal.

From the above examples, it will be noted that the rate of removal of the tin varies with the percentage of tin in the dross containing the litharge, tin oxide, etc., where the other factors are the same. For instance, in Example 1 the rate of tin removal in pounds per hour per ton of metal for the whole run is 24.37 lbs. per hour per ton of metal. In Example 2, which was conducted under comparable circumstances, similar sized apparatus, except that the amount of tin in the dross at the start was 28.57% as compared with zero per cent tin in the dross for Example 1, the rate of removal of the tin for the whole run-was 17.87 lbs. per hour per ton of metal. Thus, the higher tin content of the layer of dross added at the start of the operation slowed the rate of tin removal by'the difierence between 24.37 lbs. and 17.87 lbs., showing a drop in the rate of removal or about 27%. However, in Example 1, a dross containing only 23.05% tin was made, whereas in Example 2 a dross containing 37.49% tin was made. This at once illustrates that when using litharge, a lower grade dross is obtained with high rate of removal, whereas by using a dress already containing appreciable amounts of tin a higher grade tin dross is ob-- tained with a lower rate of removal. Similarly, Example 3, which was conducted on a larger scale apparatus with a larger quantity of lead to be purified, was treated witl a litharge, tin-oxide dross containing 11.84% tin, and showed at the end of the operation a tin removal in pounds per hour per ton of metal of 7.65 pounds for the whole run. This figure is comparable with the results in Example 4 where the same apparatus and substantially the same quantity of impure metal was treated. but the tin content of the dross added as a layer at the start of the operation was approximately 47.12% of tin. The difference in the rates between Examples 3 and 4 is accounted for not only because of the difl'erence of the tin content in the dross layer added, but, in the case of Example 3, the rate has been accelerated somewhat by the presence of a considerable proportion of antimony in the dress and metal.

In accordance with my process, I find that there is a very definite advantage in having arsenic and antimony present both from the standpoint of the rate of removal of the tin and also of the tin content of the dross obtained.

Furthermore, in accordance with a statement made above, the amount of lead removed from the bath during the operation depends on the quantity of litharge initially added to the bath. other factors being the same. It is also true that the amount of tin removed per ton of bullion, per hour, varies with the amount of litharge initially added to the bath, when the apparatus and other conditions are maintained substantially the same. In order to demonstrate this, a series of tests were run corresponding in their conditions substantially to those in Example 1 above. These tests were each run on several tons'of commercial with bullion and although there were small variations in the content of the tin and antimony, these variations were never larger than about 5% tin content and approximately 2% antimony content. The following tables accordingly show the results of the additions .of varying amounts of litharge upon the removal of lead from the bath and the pounds of tin removed per ton of bullion per hour:

Tin con- Pure Weight 'limc lost tamed and lithargc bullion removed ircatcd Pounds Pounds Pounds lvlinutes Pounds Sn Pounds dross Pounds Pb To removedpcr produced per removed per ton bullion pound Sn pound Sn per hour removed removed From the above, it will be noted that the pounds of lead removed per pound of tin removed decreases according to the initial addition of litharge to the bath, reaching a minimum in the above table where 300 pounds of litharge are initially added and showing actual increase of lead in the bath when 400 pounds of litharge were initially added. Accordingly, somewhere between 300 and 400 pounds of litharge added would result in removing substantially no lead from the bath. With respect to the pounds of tin removed per ton of bullion per hour, it will be noted that this reaches a maximum with the initial addition of about 200 pounds of litharge and from there on the increasing amounts of litharge produce gradually decreasing amounts 1 of tin removed per ton of bullion per hour. If

instead of such litharge, dross containing tin oxide and small amounts of other impurities are employed, there would be a corresponding change in the pounds of lead removed per pound of tin removed and in the pounds of tin removed per ton of bullion per hour.

In the claims, the expression lead oxide" is intended to refer to lead oxide either alone or combined with antimony or arsenic oxides and small quantities of other impurities. As shown in the above examples, where a dross is employed, the quantity of tin as oxide may run upwards of about 47%, more or less.

While the invention has been described in detail according to the preferred manner of carrying'out the process, it will be obvious to those skilled in the art after understanding the invention, that changes and modifications may be made therein without departing from the spirit or scope of the invention, and it is intended in the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent, is;

1. A process for detinning a mass containing metallic lead and tin which comprises adding a layer of previously prepared lead oxide to the mass in powdered unfused condition, heating the to replace lead oxide used up in said reaction and also to oxidize directly further quantities of tin, thereby removing tin from the bath as tin oxide.

2. A process for detinning a mass containing metallic lead and tin which comprises covering the mass with a layer of comminuted unfused lead oxide, heating the mass to liquefy the metal if necessary, stirring it with the said layer at a speed of at least 900 R. P. M. and at a temperature above approximately 950 F. to produce a reaction between lead oxide and metallic tin of the bath, said layer being of substantial thickness but of a character capable to admit air through spaces between its particles 50 that lead oxide is formed by the air to replace lead oxide used up by said reaction and also to oxidize directly further quantities of tin, thereby removing tin from the bath as tin oxide.

3. A process for detinning a mass containing metallic lead and tin which comprises adding a layer of powdered dross containing lead oxide and a substantial amount of tin oxide, heating the mass if necessary to melt the metal and to form a bath thereof, and stirring the bath and dross at a speed of at least 900 R. P. M. and at a temperature above approximately 950 F. to force the dross and some air into the bath, said layer being ofsubstantial thickness but of a character capable to admit air through spaces between its particles so that lead oxide is formed by the air to replace lead oxide used up by said reaction and also to oxidize directly further quantities of tin, thereby removing tin from the bath as tin oxide.

4. A process for detinning baths containing metallic lead and tin which comprises adding a layer of previously prepared comminuted unfused lead oxide'containing some tin oxide if desired and stirring the bath at a stirring speed of about 900 to 1800 R. P. M. and at a temperature above approximately 950 F. but below the fusion temperature of said layer to produce a reaction between lead oxide and metallic tin of the bath, said layer being of substantial thickness but of a character capable to admit air through spaces between the particles so that enough lead oxide is formed by the air to replace the lead oxide used up by said reaction and also to oxidize directly further quantities of tin, thereby removing tin from the bath as tin oxide.

5. A process for detinning baths containing metallic lead and tin which comprises taking a lead bath containing tin and other metals in a quantity up to about 20%, adding a layer of previously powdered unfused prepared litharge containing some tin oxide if desired and stirring the bath with the said layer at a speed of about 900 to about 1800 R. P. M; and at a temperature of above about 950 F. but below the complete fusion point of the layer, the layer being maintained at a thickness to admit suflicient air to replace the lead oxide used up by reaction between lead oxide and metallic tin of the bath and for direct oxidation of further quantities of tin.

6. A process for detinning baths containing metallic lead and tin which comprises taking a lead bath containing tin and other metals, adding a layer of powdered dross thereto containing litharge and tin oxide with a proportion of tin in the total dross of at least 40% and stirring the bath with the said layer at a speed of about 900 to about 1800 R. P. M. and at a temperature of above about 950 F. but below the complete fusion point of the layer, the layer being maintained at a thickness to admit sufllcient air to replace the lead oxide used up by reaction between lead oxide and metallic tin of the bath and for direct oxidation offurther quantities of tin, whereby a dross is formed containing at least 5 about 50% of tin as tin oxide.

HARVEY M. BURKEY.

CERTIFICATE OF CORRECTION. Patent No. 2, 2141,80 6. May .15, 1914.1.

HARVEY M. BURKEY.

It is hereby certified that error appears in the printed specification of the above numhered patent requiring correction as follows: Page '5, second column, line. 61, claim 5, for the words "powdered unfused prepared litharge read -'-prepared powdered Imf sed litharge--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of July, A. D. 1911.1.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

